Lexical Ambiguity in Sentence Comprehension By R. A. Mason & M. A. Just Brain Research 1146 (2007) 115-127 Presented by Tatiana Luchkina
Dec 15, 2015
Lexical Ambiguity in Sentence Comprehension
By R. A. Mason & M. A. Just Brain Research 1146 (2007) 115-127
Presented by Tatiana Luchkina
Background • Lexical ambiguity demands the reader to select
one Mg & retain the possibility of using another Mg at the same time;
• This ability is correlated with the memory capacity of the reader + the frequency of the ambiguous W Mgs;
• Correct analysis requires inhibition of the alternative Mg, erroneous analysis – creates a garden path effect;
Lexical Ambiguity• Biased: a word’s Mgs are asymmetric in
frequency, e.g., • This time the ball was moved ….….because it was always so well attended • Balanced: two equally likely Mgs, e.g., …the cell looked small…. because it was piled high with supplies
Ball Cell
Garden path effect Multiple Mgs maintained
Q: Which ambiguity type takes longer to process??
Previous studies of Lexical Ambiguity• Majority were grounded in behaviorist
tradition, measuring: • Reading times/response times • Eye movements • Cross-modal priming effects
How about brain activity during the processing of lexical ambiguity?
Ambiguity & the brain
• Left Hemisphere – rapid fine semantic coding (only relevant Mgs);
• Right Hemisphere – slow coarse semantic coding (activates a broad spectrum of meanings);
Left inferior frontal gyrus
Lefttemporal lobe
Left inferior temporal cortex & right inferior frontal cortex
de-contextualized semantic analysis;
categorization tasks
contextualized semantic processing;
Study
• Brain imaging (fMRI) used to measure brain activity during the reading of Ss with lexically-ambiguous words vs. matched control words;
• Rationale: to measure brain activity when ambiguity occurs in early (biased) or late (unbiased) selection of meaning;
• How: brain responses to the processes of ambiguity resolution relate to individual differences in working memory capacity
Experiment:
• 12 right-handed volunteer college students;• Stimuli: 36 sentences (ambiguous vs. control) with the
target appearing before any disambiguating context;
• Sentences presented on the screen 1 W at a time, at a normal reading rate; A yes/no comprehension Q followed;
• Cerebral activation measured using blood oxygenation level contrast;
Dep & Indep Variables: degrees & areas of cortical activation; individual’s working memory capacity; ambiguity types;
Findings
• Lex. Ambiguity evokes extra processing due to generation, retention, selection of multiple meanings and coherence monitoring;
• Reading of ambiguous Ss activated left inferior frontal gyros more than reading of control Ss;
• Biased condition only produced additional activation clusters in inferior/superior frontal regions of both hemispheres;
• Activation in the right hemisphere - spillover of processing to help resolve secondary Mgs;
Findings, cont’d. • Activation patterns were correlated with the
reading spans of the subjects, which reflected their working memory capacity;
• Readers with lower reading spans use right hemisphere, esp. right inferior frontal area, to resolve ambiguities & maintain multiple meanings during disambiguation;
• Bilateral extra activation occurs selectively & is minimal in the high-span subjects;